1. Field of the Invention
The present invention relates to the field of ice detectors and more particularly to ice detectors utilizing the vibration characteristics of piezoelectric transducers.
2. Description of the Prior Art
Ice detectors in the prior art determine frequency changes of virbrating diaphragm, positioned on a surface to establish ice formation on that surface. These diaphragms are driven by electromagnets energized by an alternating current source at a predetermined frequency or by an energized piezoelectric transducer vibrating at its natural frequency. As the ice accumulates the vibration frequency of the diaphragm is altered. When this frequency variation exceeds a predetermined value an indication that ice has formed on the surface is provided. In the devices utilizing piezoelectric transducers the load on the diaphragm alters its vibration frequency causing the second diaphragm, coupled to a second piezoelectric transducer, to vibrate. The vibration of the second diaphragm induces vibrations in the piezoelectric transducer coupled thereto , which in turn provides a signal indicative of such vibrations. This coupling arrangement provides a device that is needlessly complex. Frequency changes of a piezoelectric transducer will occur when it has a surface directly exposed to the environment. Further, the continuous vibrations impede ice accretions on the diaphragm, thus adversely affecting the accuracy of the measurements. Additionally, frequency variations occur with loading changes on the diaphragm or transducer, thus providing ice formation indications when matter, other than ice, establish the load. The possibility of false ice warnings, when ice in fact has not formed on the surface, render the warnings suspect.